These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: As noted under Artistic Licence Religion, Thorn being 1/16th Wiccan is complete nonsense. However she still clearly practices some elements of Wicca which arguably still makes her the best chance to defeat Sarah.
Also, Ben Ravencroft first heard about Mystery Inc from their solving the mystery of the "Moat Monster". The Moat Monster was the same story that Daphne brought up in her interview towards the beginning of Zombie Island, which means 'The Witch's Ghost' takes place in the same universe as 'Zombie Island'. However, Fridge Logic arises when you realize that Ravencroft wouldn't have waited however many years between Mystery Inc's initial retirement and their eventual revival just to get that specific team of kids to help him. After all, what would Ravencroft have done if the gang never got back together?
Ensemble Darkhorse: The Hex Girls proved to be very popular and have become recurring characters in the franchise ever since.